Maks spent his first night in Aunt Hela's lighthouse. The storm rumbled and the fog siren wailed like a huge dog. The glass of the great lens spun and cut the darkness. - 'Keep an eye on the light,' Hela said, disappearing into the doorway to the generator. - If it goes out, call out on the radio immediately. Maks was left alone with the movement of the light and the rumbling of the sea. An old lighthouse keeper's notebook, full of light codes, lay on the desk. The boy flipped through the pages, because he liked puzzles and signs. Then a strange green light flashed through the mist from the bay. It didn't match the map, or the usual lighthouses on the coast. It blinked three times, paused, again, and again three times. Maks compared it with his notes and froze at the margin. A clear word was coming out in code: DON'T WALK. A slow chain rang metallically from below, as if someone had moved it. A slight ripple passed underfoot, though the floor was cement. Maks pushed back the flap of the stairs and felt a cool, salty draught. Wet footprints were darkening on the concrete, leading from the warehouse tunnel. The warehouse door was locked and the key was stuck on our side. - Auntie? - He called out into the radio. - Over? The radio whined and a voice very similar to Hela's rang out. - Max, come downstairs immediately. The light needs to be switched off. The boy looked at the lens, which had just accelerated its rotation for no reason. The notebook still showed the warning: DO NOT GO DOWN. Behind the warehouse door something knocked once, then a second, closer. The key in the lock moved by itself and began to turn slowly.